In vivo spatial coordination with synthetic paracrine signaling

Paracrine signaling allows multiple cell types to spatially confine potent responses such as inflammation. A synthetic paracrine signaling system could circumvent cell therapy challenges such as on-target, off-tumor toxicity. However, a synthetic paracrine system that operates in vivo has been lacking. Here, using the plant hormone auxin as a bio-orthogonal signal, we introduce programmable paracrine circuits that distribute sensing and effector functions to different cell types to spatially restrict responses in mouse xenografts. Expression of auxin biosynthetic genes generated auxin-dense regions with tunable lengthscales in vivo. We then engineered a synthetic "synthacrine" circuit composed of two cell types: (1) sentinel cells that conditionally produce auxin in response to a heterogeneous cancer-specific antigen EGFRvIII, and (2) effector cells expressing an engineered, auxin-dependent chimeric antigen receptor (CAR). The full system achieved spatial confinement of CAR-T cell activation in vivo. These results provide a foundation for future multicellular therapeutic systems that focus responses at disease sites.